This invention relates to the field of spin coating, specifically spin coating apparatus commonly used in semiconductor fabrication.
In the semiconductor processing industry, materials such as photoresist are commonly applied to semiconductor wafers using a spin coating apparatus. See Neoh, U.S. Pat. No. 5,562,772; Cardinali, U.S. Pat. No. 5,449,405; Cardinali, U.S. Pat. No. 5,378,511; Lin, U.S. Pat. No. 5,366,757; Hurtig, U.S. Pat. No. 5,289,222. The wafer is placed on a flat vacuum chuck and spun while the material is applied through a nozzle near the center of the wafer. When the wafer is spun at high speed, centrifugal force causes the material to flow toward the circumference of the wafer, covering the wafer with a smooth, even coat of material. FIG. 1 shows a cross sectional view of a conventional spin coating apparatus.
During the spin coating process, a pump attached to exhaust port X1 draws cleanroom air into catch cup C, over the exposed wafer surface, into exhaust outlet X2, through exhaust duct X4 and out of the spin coating apparatus into the fab exhaust system. An additional flow path X3 allows cleanroom air to flow along the wafer underside into exhaust outlet X2 to minimize contamination of the wafer underside. Excess material is spun off the wafer into exhaust outlet X2, where it is trapped below the plane of the wafer surface. A primary concern is contamination of the cleanroom environment by material such as volatile photoresist solvent. Cleanroom air flow as described above can transport much of the excess material to exhaust outlet X2. With conventional spin coating apparatus, high cleanroom air flow rates can be required to prevent unacceptable cleanroom environment contamination. Cleanroom air is costly, however, and excessive cleanroom air flow contributes to excessive operating and environmental costs. Accordingly, there is a need for an improved spin coating apparatus that minimizes cleanroom contamination while requiring reduced cleanroom air flow.